What is the use cases of Ignored Variable syntax in Scala?

Question

According to this answer https://stackoverflow.com/a/8001065/1586965 we can do this in Scala:

val _ = 5

Now I understand the point of ignor

Answer 1

It uses a value.

$ scala -Ywarn-value-discard
Welcome to Scala version 2.11.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_11).
Type in expressions to have them evaluated.
Type :help for more information.

scala> def f() = { println("I ran.") ; 42 }
f: ()Int

scala> def g(): Unit = { f() }
:8: warning: discarded non-Unit value
       def g(): Unit = { f() }
                          ^
g: ()Unit

scala> def g(): Unit = { val _ = f() }
g: ()Unit

scala> g
I ran.

scala> 

To verify, it also doesn't warn under -Ywarn-unused.